The present invention generally relates to couplings by which two structures can be coupled together, and particularly to fifth wheel couplings adapted to secure trailers to tow vehicles.
Fifth wheel couplings are widely used as the connection between trailers, such as a semi-trailer, and vehicle adapted for towing trailers, such as a towing truck, tractor, recreational vehicle, etc. As used herein, the terms “trailer” and “vehicle” encompass, respectively, a wide variety of mobile equipment adapted to be directly or indirectly towed by a wide variety of self-propelled vehicle. Fifth wheel couplings typically comprise a downwardly-projecting coupling pin (commonly referred to as a kingpin) beneath the front end of a trailer, and a horseshoe-shaped coupling device (commonly referred to as the fifth wheel) located near the rear end of the vehicle. The kingpin is mounted to a trailer with what is commonly known as an upper coupler assembly. Upper coupler assemblies are typically made up of channel and/or angle iron and one or more plates, which are typically welded together to form an assembly that can be welded, bolted or secured in some other manner to a structural part of a trailer. Loads imposed on a kingpin are transferred to and from a trailer through its upper coupler assembly, such that upper coupler assemblies are subjected to considerable loads.
Because of the harsh environment encountered on roads and highways, especially as a result of the presence of salts and chemicals intended to melt snow and ice, as well as the corrosiveness of some materials hauled on a trailer, upper coupler assembly are subject to corrosion that can lead to structural failure. While mandatory inspections of coupler assemblies are a common practice, the effectiveness of these inspections is limited by the difficulty of quickly and reliably inspecting the integrity of the multiple joints that hold a coupler assembly together and to a trailer.